The present invention relates to methods and apparatus for improving the stability of RF power delivery to a plasma load in a plasma processing system.
Plasma processing systems have been around for some time. Over the years, plasma processing systems utilizing inductively coupled plasma sources, electron cyclotron resonance (ECR) sources, capacitive sources, and the like, have been introduced and employed to various degrees to process semiconductor substrates and glass panels.
During processing, multiple deposition and/or etching steps are typically employed. During deposition, materials are deposited onto a substrate surface (such as the surface of a glass panel or a wafer). For example, deposited layers comprising various forms of silicon, silicon dioxide, silicon nitride, metals and the like may be formed on the surface of the substrate. Conversely, etching may be employed to selectively remove materials from predefined areas on the substrate surface. For example, etched features such as vias, contacts, or trenches may be formed in the layers of the substrate. Note that some etch processes may utilize chemistries and/or parameters that simultaneously etch and deposit films on the plasma-facing surfaces.
The plasma can be generated and/or sustained using a variety of plasma generation methods, including inductively-coupled, ECR, microwave and capacitively-coupled plasma methods. In an inductively-coupled plasma processing chamber, for example, an inductive source is employed to generate the plasma. To facilitate discussion, FIG. 1 illustrates a prior art inductive plasma processing chamber 100, which is configured for etching in this example. Plasma processing chamber 100 includes a substantially cylindrical chamber wall portion 102 and an antenna or inductive coil 104 disposed above a dielectric window 106. Typically, antenna 104 is operatively coupled to a first radio frequency (RF) power source 108, which may include an RF generator 110 and an RF match network 112 as shown. RF generator 110 may operate at a frequency of, for example, 4 MHz. Generally speaking, the RF signals from the RF generators may be sinusoidal, pulsed, or non-sinusoidal. Dielectric window 106 is typically formed of a high resistivity dielectric material, such as high resistivity silicon carbide (SiC).
Within plasma processing chamber 100, a set of inlet gas ports (not shown) is typically provided to facilitate the introduction of gaseous source materials, e.g., the etchant source gases, into the RF-induced plasma region between dielectric window 106 and a substrate 114. Substrate 114 is introduced into chamber 100 and disposed on a chuck 116. Chuck 116 generally acts as an electrode and is operatively coupled to a second RF power source 118, which may include an RF generator 120 and an RF match network 122 as shown. RF generator 120 may operate at an RF frequency of, for example, 13.56 MHz. As mentioned, the RF signal from RF generator 120, like other RF signals from the RF generators, may be sinusoidal, pulsed, or non-sinusoidal.
In order to create a plasma, a process source gas is input into chamber 100 through the aforementioned set of inlet gas ports. Power is then supplied to inductive coil 104 using RF power source 108 and to chuck 116 using RF power source 118. The supplied RF energy from RF power source 108 coupled through dielectric window 106 excites the process source gas and a plasma 124 is generated thereby.
Chamber 100 may also be provided with different components, depending on the specific manufacturer thereof and/or the requirements of a particular process. For example, focus rings, plasma screens, magnets, pressure control rings, hot edge rings, various gas injector nozzles, probes, chamber liners, etc., may also be provided. To simplify the illustration, these well-known components are omitted from FIG. 1.
Generally speaking, it is critical to maintain tight control of the etch process in order to obtain a satisfactory etch result. Thus, parameters such as the antenna RF voltage, antenna RF power, bias RF voltage, bias RF power, plasma density, the amount of contamination in the chamber, and the like, must be carefully controlled. Furthermore, it is important to maintain a tight control of the etch process over as wide a process window as possible. In this regard, the stability of the RF power delivery to the plasma load is a particularly important issue. For a given process recipe, it is crucial that the RF power delivery remain stable throughout the process to obtain a reliable process result.
This invention deals with methods and apparatus for improving the stability of the RF power delivery to the plasma in a plasma processing chamber as well as methods for quantifying parameters contributing to the stability of the RF power delivery to the plasma at a given parameter setting.